This is a Phase I/II, (Abbot 378) dose-blinded, multi-center study of ABT-378/ritonavir in combination w/stavudine (d4T) & lamivudine (3TC) in otherwise healthy HIV-infected males and females. The primary objective of this study is to assess the safety, tolerability, and antiviral activity of ABT-378/ritonavir when administered orally in antiretroviral naive HIV-infected patients. The secondary objective is: 1) to determine steady-state pharmacokinetic profile of ABT-378/ ritonavir in antiretroviral naive HIV-infected patients and 2) to assess the relationship between ABT-378/ritonivir and HIV RNA decay profiles in antiretroviral naive HIV-infected patients.